A special committee under the Transport Ministry ordered the Teito Rapid Transit Authority to inspect all subway cars of the same type as the one that was involved in the fatal accident near Tokyo's Nakameguro Station on Wednesday morning.
The committee of experts did not specify the cause of the derailment in the day's meeting.
"I get the impression that it's quite difficult to specify the cause at this stage," said Masatomi Yasutomi, chief of the ministry's railway bureau, who attended the committee session. "I think the committee members are of the same impression."